Chairs comprising a backrest frame, a fixed base frame having the seat constrained thereto and a mechanism for adjusting the seat when the tilt of the backrest changes with respect to the seat itself, are known in the art.
Usually, a covering element made of various materials is placed above the seat and can fully cover the seat on which, once upholstered, the user will sit.
However, the adjusting mechanisms used in such a chairs do not allow the position of the seat to be changed when the tilt of the backrest changes in order to prevent the user from experiencing an uncomfortable feeling of “sinking” in the seat or moving toward the front edge of the latter, in various backrest tilts.
To overcome this drawback, chairs provided with adjusting mechanisms comprising means for synchronizing the position of the seat with respect to that of the backrest, are known. For example, such synchronizing means are provided with a first frame which can be combined with the backrest, or backrest frame, a second frame which can be combined with the seat, or seat frame, movably constrained to the aforesaid base frame of the chair, and a mechanism for synchronously moving said first frame and said second frame with respect to one another. Such synchronizing means are described, for example, in the European Patent EP2375938B1 in the name of the Applicant.
Such synchronizing means, described in the above mentioned Patent, are very efficient and provide both the technical effect of synchronizing the movement of the seat to that of the chair backrest, and the effect of preventing the user from feeling to “sink” in the seat or to slide outside the latter, when the backrest is in its maximum reclined position. The particular synchronization mechanism described in the above-mentioned Patent allows the achievement of this result because, when the backrest is partially or fully reclined, the seat, being anyway movable with respect to the base frame of the chair, moves so as to maintain the height of its front portion always slightly lower than the height reached by the rear portion.
However, the drawback of the herein described synchronizing means is their complexity and the use of a large number of mutually movable components. In particular, the seat always comprises a fixed base frame and a movable seat frame which is somehow constrained to the base frame and moves with respect to it.
Thus, for example, the aforementioned adjusting mechanism of the synchronizing type, is not very suitable for traditional chairs having four fixed side legs, since these have to be made so as to limit the number of components and their structural and operational complexity, for allowing to be constructional simple and therefore to be cost effective.
It is therefore an object of the present invention to provide an adjusting mechanism for adjusting the seat of a chair when the tilt of the backrest changes, which can apply to any kind of chair and prevents the user from feeling uncomfortable when the tilt of the backrest changes with respect to the seat.
It is a further object of the present invention to provide a mechanism, and therefore a chair, which is structurally simple and easy to be assembled while allowing in any case to effectively change the tilt of the backrest with respect to the seat.